Both aging and the usually acompanying exposure to ultraviolet light cause deterioration of the visual system and there is evidence of synergy. Age related decline in human visual performance is well documented and some decrements may be due to anatomical changes in the retina. This is a proposal to develop the necessary quantitative methods to evaluate and eventually understand the effects of aging and ultraviolet light exposure on the ganglion cell layer of the rhesus monkey retina. This study is made possible by the availability of a unique population of rhesus monkeys of the same genetic stock that live outdoors in Puerto Rico. The rhesus monkey retina is a good model of the human retina. In the ganglion cell layer of both rhesus and humans two types of neurons (ganglion cells and displaced amacrine cells) have been described along with two types of glia (astrocytes and microglia). The research proposed here will develop methods to explore quantitative changes in the ganglion cell layer during aging in rhesus monkeys raised in Puerto Rico. The density and soma size spectra of the four cell types found in the ganglion cell layer will be studied independently in rhesus monkeys of various ages. Preliminary data indicate possible gliosis and loss of ganglion cells in older rhesus monkeys raised in Puerto Rico. These observations contrast with a recent report indicating no loss of ganglion cells in older rhesus monkeys raised in Wisconsin and suggest that the relatively harsh photic environment of Puerto Rico, which includes high levels of ultraviolet light, may cause or exaggerate changes in the ganglion cell layer during aging. Anatomical changes in the retina during aging are of special interest since the human population of the United States is rapidly aging. An additional deleterious effect of ultraviolet radiation on the retina has significance for public health education.